Silicon semiconductor substrate

ABSTRACT

The present invention can provide a silicon semiconductor substrate used for and epitaxial wafer, in which uniform and high-level gettering ability is obtained irrespective of slicing positions from a silicon single crystal while generation of epitaxial defects can be suppressed, by doping carbon or carbon along with nitrogen during a pulling process of a CZ method or by performing appropriate heat treatment prior to the epitaxial process. Therefore, a crystal production yield can remarkably be improved because a permissible upper limit (concentration margin) of an oxygen concentration which is restricted by formation of a ring-shaped OSF region can be higher and also an excellent gettering ability is exhibited, while allowing an epitaxial wafer to be produced wherein epitaxial defects attributable to substrate crystal defects are not formed.

FIELD OF THE INVENTION

The present invention relates to a silicon semiconductor substrate usedfor an epitaxial wafer (p/p⁺ epitaxial wafer) in which boron is doped inhigh concentration and a production method thereof, and moreparticularly, to the silicon semiconductor substrate and productionmethod thereof, in which a defect (hereinafter referred to as “epitaxialdefect”) attributable to a substrate crystal defect is not generated inan epitaxial layer while formation of oxygen precipitates (BMD: a bulkmicro defect) is promoted by doping carbon or carbon along with nitrogenin a pulling process of the Czochralski method (hereinafter referred toas “CZ method”).

DESCRIPTION OF THE RELATED ART

The scale of integration is rapidly increased in a silicon semiconductorintegrated circuit device. With the development of a finer circuit to beformed, crystal defects such as dislocation—causing an increase in leakcurrent and shortening of carrier lifetime—and metal impurities exceptfor a dopant need to be much more strictly controlled than ever beforein a device active region of a silicon wafer. Therefore, an epitaxialwafer in which the silicon epitaxial layer containing almost no crystaldefects is grown has been developed and frequently used for a highlyintegrated device in order to respond to the demand for such strictcontrol.

However, when the semiconductor-device integrated circuit is operated, agenerated floating charge activates an unintended parasitic transistor,which results in creation of a phenomenon called latch-up. When thelatch-up phenomenon occurs, the semiconductor device is not normallyoperated to cause such a trouble that the power is necessarily turnedoff for restitution in integrum.

A p/p⁺ epitaxial wafer is applied as a countermeasure against thelatch-up. The p/p+ epitaxial wafer is one in which the epitaxial layeris grown on a substrate (p⁺ substrate) containing high-concentrationboron by utilizing that the p⁺ substrate has a gettering effect. Inaddition to the prevention of the latch-up phenomenon, the p⁺ substratealso prevents a depletion layer expansion, the expansion being caused byvoltage application to the surroundings of a trench when a capacitorhaving a trench structure is used. Therefore, the p⁺ substrate is widelyused because the p⁺ substrate can achieve improvement of devicefunctions.

FIG. 1 shows a distribution state of typical defects existing in asilicon single crystal produced by the CZ method. FIG. 1 schematicallyshows a observation result, in which a wafer having a surfaceperpendicular to a pulling axis is sliced from a single crystalimmediately after the growth, Cu is caused to adhere to the surface bydipping the wafer in a copper nitrate solution, and a distribution ofmicro defects is observed after heat treatment by X-ray topography.

Because the silicon single crystal grown by the CZ method containsoxygen, sometimes a ring-shaped region of oxygen induced stacking fault(hereinafter referred to as “OSF”) is generated by performing thermaloxidation treatment to the wafer sliced therefrom. The defects includinga vacancy called crystal originated particle (COP) having a size rangingfrom about 0.1 μm to about 0.2 μm and a micro dislocation calleddislocation cluster having a size of about 10 μm emerge as grown-indefects in the silicon single crystal grown by the CZ method.

For example, the defects are observed with the distribution state shownin FIG. 1 when the silicon single crystal is produced by the normal CZpulling method. Referring to FIG. 1, a ring-shaped OSF region emerges ata position of about two-third of a crystal diameter, about 10⁵ to 10⁶count/cm³ COPs are detected inside the ring-shaped OSF region, and about10³ to 10⁴ count/cm³ dislocation cluster defects are detected outsidethe ring-shaped OSF region.

FIG. 2 is a sectional view schematically showing a defect distributionstate of the single crystal which is grown while a pulling speed isgradually decreased in pulling the single crystal, and FIG. 2 also showsa general relationship between the pulling speed and the position wherethe crystal defects are generated. Usually the pulling speed during thesingle crystal growth and a temperature distribution in the singlecrystal immediately after solidification have a large influence on thedefect generation state. For example, the defect distribution stateshown in FIG. 2 can be obtained, when the single crystal which is grownwhile the pulling speed is gradually decreased is sectioned along apulling axis of the crystal center to observe the defect distribution ofthe sectional surface by the technique similar to FIG. 1.

When viewed from the surface perpendicular to the pulling axis, in anearly stage at which the pulling speed of a straight body portion isfast after a shoulder portion is formed and the single crystal comes tobe a preset diameter, the ring-shaped OSF region exists in a crystalperipheral portion and many COPs are generated at the inside of thecrystal. As the pulling speed is decreased, the diameter of thering-shaped OSF region is gradually decreased while a region where thedislocation cluster defects are generated happens to emerge outside thering-shaped OSF region, and then the dislocation cluster defectgeneration region occupies the whole surface.

FIG. 1 shows the wafer sliced from the single crystal which is grown ata position A of FIG. 2 or at the pulling speed corresponding to theposition A. In the defect distribution shown in FIG. 2, the ring-shapedOSF region exists in the crystal surface over the whole length from atop portion to a tail portion of the single crystal in the wafer slicedfrom the single crystal which is grown at positions B and C of FIG. 2 orat the pulling speed corresponding to the positions B and C.

Generally the micro defects such as the dislocation are easily generatedin the ring-shaped OSF region formed in the silicon single crystalcontaining high-concentration boron. When the epitaxial layer is grownon the wafer containing the ring-shaped OSF region formed in the siliconsingle crystal containing high-concentration boron, the crystal defectsin the wafer propagate to the epitaxial layer to generate the epitaxialdefects at the position corresponding to the ring-shaped OSF regionduring the growth process of the epitaxial layer. The presence of theepitaxial defects in the epitaxial layer which is of the device activeregion causes degradation of device characteristics, which leads to thedecrease in device production yield.

In order to cope with the above problems, Japanese Patent ApplicationPublication No. 2004-165489 proposes a method, in which the siliconsingle crystal containing the high-concentration boron is grown onvarious pulling speed conditions, the pulling speed at which thering-shaped OSF region is eliminated in a crystal center portion isdetermined from the study result of the single crystal defectdistribution to obtain the silicon single crystal having the crystalregion where the ring-shaped OSF region is eliminated in the crystalcenter portion, and thereby the epitaxial layer is grown on the wafer inwhich the ring-shaped OSF region is eliminated in the crystal centerportion.

However, in the method proposed in Japanese Patent ApplicationPublication No. 2004-165489, when the pulling condition on which thering-shaped OSF region is eliminated in the crystal center portion overthe whole length of the single crystal, there is a restraint from thestandpoint of production efficiency because the pulling speed becomesextremely slow. Therefore, it is not desirable to apply the methodproposed in Japanese Patent Application Publication No. 2004-165489 tothe method for producing the silicon semiconductor substrate whichbecomes the epitaxial wafer substrate.

Japanese Patent Application Publication No. 2003-73191 also proposes amethod in which, because micro dislocations are generated in thering-shaped OSF region of the wafer doped with nitrogen andhigh-concentration boron although the ring-shaped OSF region is not anI-rich region, the silicon single crystal for the epitaxial growth isproduced on the condition that V/G (V: pulling speed and G: temperaturegradient in an crystal axis direction near a solid-liquid interface inthe crystal) located between a lower limit value of the microdislocation generation region in the ring-shaped OSF region and an upperlimit value of the I-rich region.

However, in the method proposed in Japanese Patent ApplicationPublication No. 2003-73191, when the ring-shaped OSF region emerges inthe crystal surface over the whole length of the pulled single crystal,any consideration is not given to nitrogen and boron segregationgenerated from the top portion toward the tail portion of the siliconsingle crystal, and thus it is difficult that the gettering ability isuniformly obtained while the epitaxial defects are decreased over thewhole single crystal.

SUMMARY OF THE INVENTION

In the growth of the silicon single crystal containing thehigh-concentration boron by the CZ method, when the growth is performedon the condition that the ring-shaped OSF region emerges in the crystalsurface over the whole length of the pulled single crystal, the boronconcentration is increased over the whole length of the single crystal,particularly in the tail portion due to the boron segregation, and theepitaxial defects are generated, in association with an influence of athermal history, in the ring-shaped OSF region during the epitaxialgrowth process.

And in the case where the silicon single crystal contains nitrogen,because a BMD density largely depends on the slicing positions from thesilicon single crystal due to the nitrogen segregation in the growth bythe CZ method, the uniform gettering ability is hardly obtained over thewhole length of the single crystal, and the epitaxial defect generationstate is also changed in the epitaxial wafer according to the slicingposition from the silicon single crystal.

Then, in producing the epitaxial wafer, because of high temperaturesranging from 1050° C. to 1200° C. during an epitaxial layer growthprocess, BMDs which should become a nucleus of the micro defects in thesubstrate are reduced and eliminated, and the sufficient number of microdefects which become gettering sources are hardly induced into the waferin the subsequent device process. Particularly, when the device processis performed at lower temperatures, because a growth rate of BMD becomesslower, the sufficient gettering ability cannot be exhibited not only inthe initial stage of the device process but over the whole deviceprocess.

In view of the foregoing problems regarding epitaxial wafer, the presentinvention is attempted, and its object is to provide a siliconsemiconductor substrate and a production method thereof in which, in anyepitaxial wafer substrate, the uniform and high-level gettering abilitycan be obtained irrespective of the slicing positions from the siliconsingle crystal while the generation of the epitaxial defects issuppressed, by doping carbon or carbon along with nitrogen during thepulling process of the CZ method and/or by performing the appropriateheat treatment prior to the epitaxial process.

In the case where the single crystal is grown on the condition that thering-shaped OSF region emerges in the crystal surface over the wholelength of the pulled single crystal, the formation of the ring-shapedOSF region can be suppressed when the carbon is doped during the pullingprocess.

Hence, such a carbon doping effect of suppressing the formation of thering-shaped OSF region is incorporated over the whole length of thesingle crystal where the ring-shaped OSF region should emerge, whichallows defect characteristics to be moderated and used as a product evenin the region where the defect characteristics of the ring-shaped OSFregion should become conspicuous due to the boron segregation or theinfluence of the thermal history in the tail portion of the singlecrystal.

And, in the case where the nitrogen is doped, the nitrogen is segregatedfrom the top portion toward the tail portion of the grown singlecrystal, the nitrogen concentration varies over the whole length of thesingle crystal, and thereby the gettering ability fluctuates to easilygenerate the epitaxial defects in the tail portion. Even in this case,the fluctuations can be moderated to exhibit the uniform getteringability over the whole length. The present invention can be completedbased on the findings and expertise of the carbon doping.

Thus, a silicon semiconductor substrate according to the presentinvention, is characterized in that, so as to be better fitted to anepitaxial wafer substrate, the silicon semiconductor substrate is grownby the Czochralski method on a condition that a ring-shaped oxygeninduced stacking fault region emerges in a crystal surface over a wholelength of a straight body portion of a pulled silicon single crystal,and the silicon semiconductor substrate is sliced from the siliconsingle crystal in which boron ranging from 1×10¹⁷ to 1×10¹⁹ atoms/cm³and carbon ranging from 1×10¹⁵ to 2×10¹⁶ atoms/cm³ (ASTM F123-1981) aredoped.

Further, a silicon semiconductor substrate according to the presentinvention is characterized in that the silicon semiconductor substrateis grown by the Czochralski method on a condition that a ring-shapedoxygen induced stacking fault region emerges in a crystal surface over awhole length of a straight body portion of a pulled silicon singlecrystal, and the silicon semiconductor substrate is sliced from thesilicon single crystal in which boron ranging from 1×10¹⁷ to 1×10¹⁹atoms/cm³, carbon ranging from 1×10¹⁵ to 2×10¹⁶ atoms/cm³(ASTMF123-1981), and nitrogen ranging from 5×10¹² to 5×10¹⁴ atoms/cm³ aredoped.

Thus, the fluctuation of characteristics over the whole length of thesingle crystal associated with the boron segregation and the nitrogensegregation is alleviated by doping the carbon in the siliconsemiconductor substrate of the present invention, so that the uniformand high-level gettering ability can be obtained irrespective of theslicing positions from the silicon single crystal while the generationof the epitaxial defects is suppressed.

In the silicon semiconductor substrate by the present invention, thesilicon semiconductor substrate may be sliced from the silicon singlecrystal which is grown while an oxygen concentration ranges from 9×10¹⁷to 16×10¹⁷ atoms/cm³ (ASTM F121-1979). The formation of the ring-shapedOSF region emerging in the crystal can be suppressed by doping carbonduring the pulling process. Therefore, the permissible upper limit(concentration margin) of the oxygen concentration which is restrictedby the appearance of the OSF nuclei can be much higher, and the devicecharacteristics are not degraded even in the intermediate oxygenconcentration level or high oxygen concentration level.

In the silicon semiconductor substrate by the present invention, adensity of oxygen precipitates (BMD) in a cross section of a siliconsubstrate sliced from the silicon single crystal can be not lower than1×10⁴ count/cm² in any position over the whole length of the straightbody portion of the single crystal, whereby the uniform and high-levelgettering ability can be secured.

A silicon semiconductor substrate according to the present invention ischaracterized in that an epitaxial defect attributable to a crystaldefect of the silicon semiconductor substrate does not exist on asurface of an epitaxial layer in any position over the whole length ofthe straight body portion of the pulled single crystal when theepitaxial layer is formed on the silicon semiconductor substrate. Thegeneration of the epitaxial defect can be suppressed even in the tailportion of the single crystal by applying the carbon doping effect ofsuppressing the formation of the ring-shaped OSF region over the wholelength of the single crystal.

A method for producing a silicon semiconductor substrate according tothe present invention is characterized in that so as to be better fittedto an epitaxial wafer, the silicon semiconductor substrate is slicedfrom a silicon single crystal, the silicon single crystal being grownwhile boron ranging from 1×10¹⁷ to 1×10¹⁹ atoms/cm³ and carbon rangingfrom 1×10¹⁵ to 2×10¹⁶ atoms/cm³ (ASTM F123-1981) are doped on acondition that a ring-shaped oxygen induced stacking fault regionemerges in a crystal surface over a whole length of a straight bodyportion of a pulled silicon single crystal by the CZ method.

Further, a method for producing a silicon semiconductor substrateaccording to the present invention is characterized in that the siliconsemiconductor substrate is sliced from a silicon single crystal, thesilicon single crystal being grown while boron ranging from 1×10¹⁷ to1×10¹⁹ atoms/cm³, carbon ranging from 1×10¹⁵ to 2×10¹⁶ atoms/cm³, andnitrogen ranging from 5×10¹² to 5×10¹⁴ atoms/cm³ (ASTM F123-1981) aredoped on a condition that a ring-shaped oxygen induced stacking faultregion emerges in a crystal surface over a whole length of a straightbody portion of a pulled silicon single crystal by the CZ method.

Thus, in the silicon semiconductor substrate production method by thepresent invention, the characteristics fluctuation over the whole lengthof the single crystal associated with the boron segregation and thenitrogen segregation is alleviated by doping the carbon during thepulling process, so that the uniform and high-level gettering abilitycan be obtained irrespective of slicing positioned from the siliconsingle crystal while the generation of the epitaxial defect issuppressed.

In the method for producing a silicon semiconductor substrate by thepresent invention, a heat treatment may be performed to the siliconsubstrate sliced from the silicon single crystal, at 700° C. to 900° C.for 15 minutes to 4 hours prior to an epitaxial process. Such a heattreatment can grow precipitation nuclei that might disappear by thehigh-temperature epitaxial growth process, which allows the nuclei tonot disappear during subsequent epitaxial process and enables thedensity of retained precipitates to increase.

The method for producing a silicon semiconductor substrate by thepresent invention, can be characterized in that the silicon substrate issliced from the silicon single crystal which is grown while an oxygenconcentration ranges from 9×10¹⁷ to 16×10¹⁷ atoms/cm³ (ASTM F121-1979).Therefore, the permissible upper limit (concentration margin) of theoxygen concentration which is restricted in association with theappearance of the OSF nuclei can be much higher by the carbon dopingeffect of suppressing the formation of the ring-shaped OSF region, andthe device characteristics are not degraded even in the intermediateoxygen concentration level and high oxygen concentration level.

In the method for producing a silicon semiconductor substrate by thepresent invention, a density of oxygen precipitates in a cross sectionof a silicon substrate sliced from the silicon single crystal is notlower than 1×10⁴ count/cm² in any slicing position over the whole lengthof the straight body portion of the single crystal. Therefore, theuniform and high-level gettering ability can be secured.

In the method for producing a silicon semiconductor substrate by thepresent invention, an epitaxial defect attributable to a crystal defectof the obtained silicon semiconductor substrate does not exist in asurface of an epitaxial layer in any slicing position over the wholelength of the straight body portion of the single crystal when theepitaxial layer is formed on the silicon semiconductor substrate. Thegeneration of the epitaxial defect can be suppressed even in the tailportion of the single crystal by incorporating the carbon doping effectof suppressing the formation of the ring-shaped OSF region over thewhole length of the single crystal.

According to the silicon semiconductor substrate and the productionmethod thereof by the present invention, in any epitaxial wafersubstrate, the uniform and high-level gettering ability is obtainedirrespective of the slicing positions from the silicon single crystalwhile the generation of the epitaxial defect can be suppressed, bydoping carbon or carbon and nitrogen during the pulling process of theCZ method and/or by performing the appropriate heat treatment prior tothe epitaxial process.

Therefore, the permissible upper limit (concentration margin) which isrestricted by the formation of the ring-shaped OSF region can be muchhigher and the excellent gettering ability can be exhibited, whileenabling to make the epitaxial wafer in which the epitaxial defectattributable to the substrate crystal defect might not be generated,thereby making it possible to remarkably improve the crystal productionyield.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a distribution state of typical defects existing in asilicon single crystal produced by a CZ method; and

FIG. 2 is a sectional view schematically showing a defect distributionstate of a single crystal which is grown while a pulling speed isgradually decreased in pulling the single crystal, and FIG. 2 also showsa general relationship between the pulling speed and a position wherethe crystal defect is generated.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A silicon semiconductor substrate according to the present inventioncontains boron in high concentration. Specifically the siliconsemiconductor substrate by the present invention is grown while boron isdoped in the range of 1×10¹⁷ to 1×10¹⁹ atoms/cm³, and the siliconsemiconductor substrate is used as the epitaxial wafer substrate. Thereason why the boron concentration is not lower than 1×10¹⁷ atoms/cm³ isthat the enhancement of boron concentration increases substrate strengthwhile promoting oxygen precipitation to secure the gettering effect. Onthe other hand, when the boron concentration exceeds 1×10¹⁹ atoms/cm³,the ring-shaped OSF region emerging in the crystal surface contracts anddisappear in the crystal center portion, and the ring-shaped OSF regionis not generated in the crystal surface. However, the dislocation easilyoccurs in the single crystal ingot growth stage, and the stable singlecrystal is hardly grown, because the boron concentration of 1×10¹⁹atoms/cm³ is a solubility limit of boron to the silicon crystal.

And in the silicon semiconductor substrate by the present invention, itis essential to add carbon in the pulling process by the CZ method inorder to suppress the formation of the ring-shaped OSF region emergingin the crystal surface. Therefore, when the poly-crystalline silicon ismelted before the pulling stage of the CZ method, pure carbon is addedto adjust the carbon concentration contained in the post-pulling siliconsingle crystal.

The area where the ring-shaped OSF region is generated is the one inwhich the vacancy is dominant during the crystal growth, and a stableprecipitate nucleus exists at high temperatures in the ring-shaped OSFregion. When an oxidation treatment is performed in the ring-shaped OSFregion, excessive interstitial silicon is injected into the crystal, andthe interstitial silicon is concentrated on a strain field of oxygenprecipitates (BMD) to induce the stacking fault. Because thelattice-substitution carbon has an atomic radius of 0.66 times as big asthat of silicon, a volume is reduced and the carbon absorbs theinterstitial silicon by forming a compound (SiC) of the carbon andinterstitial silicon.

A degree of supersaturation of the interstitial silicon can be decreasedto suppress the formation of the ring-shaped OSF region emerging thecrystal surface by adding the carbon into the silicon single crystalbased on the action that the carbon absorbs the interstitial silicon.

As described above, even the tail portion, namely, the region where thedefect characteristics of the ring-shaped OSF region remarkably emergesdue to the boron segregation caused by the doping of thehigh-concentration boron and the influence of the thermal history can behealed and allowed to be used as the product by incorporating the carbondoping effect of suppressing the formation of the ring-shaped OSF regionover the whole length of the single crystal.

Similarly, even in the case where the nitrogen concentration is changedover the whole length of the single crystal due to the nitrogensegregation in doping the nitrogen, the generation of the epitaxialdefect caused by propagation of the substrate crystal defect can besuppressed in the tail portion by alleviating the influence of thechange in nitrogen concentration to achieve the uniform getteringability.

When the carbon concentration is lower than 1×10¹⁵ atoms/cm³, theformation of the ring-shaped OSF region emerging in the crystal is noteffectively suppressed. On the other hand, when the carbon concentrationexceeds 2×10¹⁶ atoms/cm³, the carbon segregation tends to be generatedin the crystal to have an influence on the substrate quality. Therefore,the carbon concentration doped in the silicon single crystal is set inthe range of 1×10¹⁵ to 2×10¹⁶ atoms/cm³ (ASTM F123-1981).

Further, in the silicon semiconductor substrate by the presentinvention, while oxygen precipitation is promoted, nitrogen can be dopedto secure the sufficient substrate strength. The effect of promotingoxygen precipitation does not exhibit when the nitrogen concentration islower than 5×10¹² atoms/cm³, and when the nitrogen concentration exceeds5×10¹⁴ atoms/cm³ to become excessive, the dislocation is easilygenerated to obstruct the growth of the single crystal. Therefore, thenitrogen concentration doped in the silicon single crystal is set in therange of 5×10¹² to 5×10¹⁴ atoms/cm³.

And, in the silicon semiconductor substrate by the present invention,the permissible amount of the oxygen concentration can be enhancedbecause the formation of the ring-shaped OSF region is suppressed by thecarbon doping. However, when the oxygen concentration is lower than9×10¹⁷ atoms/cm³, because the wafer strength cannot sufficiently besecured, a slip is easily generated and BMD density (oxygenprecipitates) becomes insufficient. On the other hand, when the oxygenconcentration exceeds 16×10¹⁷ atoms/cm³, the BMD generation and the OSFformation becomes apparent in a wafer surface portion to induce theepitaxial defect in the subsequent epitaxial layer formation, andconsequently, the device characteristics likely becomes worsened.Therefore, the oxygen concentration is preferably set in the range of9×10¹⁷ to 16×10¹⁷ atoms/cm³ (ASTM F121-1979).

In the present invention, the condition that the ring-shaped OSF regionemerges in the crystal surface over the whole length of the straightbody portion of the pulled single crystal is defined such that: thering-shaped OSF region emerging in the crystal surface can exist in thecrystal surface over the whole length from the top portion to the tailportion of the straight body portion in the grown single crystal, whilebeing neither reduced nor eliminated in the crystal center portion, whenthe single crystal is grown without doping the carbon by the CZ method.

Specifically, given that G (° C./mm) is the temperature gradient in thecrystal axis direction in the temperature range from a melting point to1370° C. and V (mm/min) is the pulling speed, the condition defined bythe present invention is that the crystal is grown while a ratio of V/Gis not lower than 0.2 mm/° C.·min.

To check whether or not the silicon semiconductor substrate by thepresent invention is sliced from the silicon single crystal grown on thecondition that the ring-shaped OSF region emerges in the crystalsurface, it is necessary to examine whether or not the ring-shaped OSFregion exists within the crystal surface by performing high-temperatureoxidation heat treatment and selective etching to the substrate slicedfrom the straight body portion of the pulled single crystal.

For said high-temperature oxidation heat treatment, a condition that thesubstrate is held at the heating temperature ranging from 1100° C. to1150° C. for one to four hours in a dry O₂ gas or wet O₂ gas atmosphere,or alternatively a two-stage heat treatment condition such that thesubstrate is held at a heating temperature ranging from 1100° C. to1150° C. for one to four hours in the dry O₂ gas or wet O₂ gasatmosphere after being held at the heating temperature ranging from 900°C. to 1000° C. for one to four hours in the dry O₂ gas or wet O₂ gasatmosphere, can be adopted.

In the silicon semiconductor substrate by the present invention, BMDdensity in the cross section of the silicon substrate sliced from thesilicon single crystal is preferably not lower than 1×10⁴/cm² in anyposition over the whole length of the pulled straight body portion. Whenthe BMD density is not lower than 1×10⁴/cm², the high-level getteringability can uniformly be exhibited over the whole length because thegettering can sufficiently be performed to Ni which is of typical sourcefor heavy-metal contamination.

Usually the heat treatment (pre-annealing) is effectively performed tothe silicon substrate at the temperature of 700° C. to 900° C. to securethe BMD density of not lower than 1×10⁴/cm² over the whole length of thepulled straight body portion. In the case where the silicon substratehas the high oxygen concentration, the equivalent BMD density can besecured even if the heat treatment (pre-annealing) is not performed.

In the silicon semiconductor substrate by the present invention, even ifthe ring-shaped OSF region emerges over the whole length of the grownsingle crystal, the crystal defect attributable to the ring-shaped OSFregion of the substrate is eliminated in any region of the pulled singlecrystal by incorporating the carbon doping effect of suppressing theformation of the ring-shaped OSF region over the whole length of thesingle crystal, which eliminates the generation of the epitaxial defectattributable to the crystal defect.

In a production method of the present invention, the growth of theoxygen precipitate nuclei and/or BMD can be promoted by performing theheat treatment to the silicon substrate at the temperature of 700° C. to900° C. prior to the epitaxial process. In other words, the oxygenprecipitate nuclei or BMD which might be eliminated by thehigh-temperature epitaxial growth is grown by the heat treatment priorto said process, which allows retained BMD density to be increasedwithout eliminating the oxygen precipitate nuclei and/or BMD in thesubsequent epitaxial process.

When the heating temperature is lower than 700° C. in the pre-epitaxialprocess heat treatment, it takes a long time to sufficiently grow theoxygen precipitate nuclei. When the heating temperature exceeds 900° C.,BMD having the relatively large size is excessively grown in the stagein which the single crystal is grown, which induces the defect in theepitaxial layer. In the high-temperature heat treatment more than 1100°C., the growth action of the oxygen precipitate nuclei does not occurwhile the number of eliminated oxygen precipitate nuclei is increased.Therefore, the heating temperature is set in the range of 700° C. to900° C. in the present invention.

The oxygen precipitate nuclei cannot sufficiently be grown when theheating time is shorter than 15 minutes in the heat treatment at thetemperature of 700° C. to 900° C. On the other hand, when the heatingtime is longer than four hours, BMD is protruded to the epitaxial layerto easily induce the defect of the epitaxial layer. Therefore, theheating time is set in the range of 15 minutes to 4 hours in the presentinvention.

Desirably the heat treatment is performed before a mirror-polishingprocess of the wafer, to which the epitaxial process is performed, suchthat a surface flaw generated in association with the heat treatment isnot left behind, for example, the flaw caused by a wafer boat is notleft behind in the surface of the wafer, the wafer boat being loadedwith wafers to be heat-treated.

EXAMPLES

The excellent effect exhibited by the semiconductor silicon wafer by thepresent invention in which the high-concentration boron is doped alongwith the carbon will be described with reference to the followingExample 1 and Example 2.

Example 1

The silicon single crystal whose straight body portion has a diameter of300 mm was grown from a silicon raw material melt in which thehigh-concentration boron and carbon are doped by the CZ method, and thewafers were sliced from three sections composed of the top portion, thebody portion (intermediate portion), and the tail portion of the singlecrystal to produce test samples. At this point, the oxygen concentrationof the test sample was separated into a low-concentration level and ahigh-concentration level. The boron concentration, the carbonconcentration, and the oxygen concentration which are contained in thetest sample were measured by a secondary ion mass spectrometry (SIMS)method.

The obtained test samples were separated into one group to which themirror polish finishing was applied to immediately perform the epitaxialgrowth process and the other group to which the epitaxial growth processis performed after the pre-epitaxial process heat treatment isperformed, followed by the mirror-polish finishing. The heat treatmentwas set at two conditions A and B. The heat treatment condition Acomprises: the test samples were loaded at 700° C.; the temperature wasraised at a rate of 5° C./min to 900° C.; the test samples were heatedat 900° C. for 30 minutes; the temperature was lowered to 700° C.; andthen the test samples were taken out. The heat treatment condition Bcomprises: the test samples were loaded at 700° C.; the temperature wasraised at the rate of 1° C./min to 900° C.; the test samples were heatedat 900° C. for 30 minutes; the temperature was lowered to 700° C.; andthen the test samples were taken out.

In the epitaxial process condition, the deposition temperature was setto 1150° C. and the epitaxial layer having a thickness of about 5 μm wasgrown on the substrate surface. The evaluation heat treatment wasperformed to the obtained epitaxial wafer at 1000° C. for 16 hours in anoxygen atmosphere. Then, the selective etching was performed to a wafercross section for five minutes with a light etching solution, and theBMD density of the wafer cross section was measured with an opticalmicroscope. The density of a light point defect (LPD) whose size was notlower than 0.09 μm was measured in the surface of the epitaxial layerwith a planar defect detector (SP1; made by Tenchor). In order to checkwhether or not the EP planar defect (LPD) observed SP1 was the defectattributable to the substrate crystal defect, the defect was evaluatedwith a transmission electron microscope (TEM) based on a coordinate ofLPD on the epitaxial layer, which was detected by SP1.

Tables 1 and 2 show the measurement results of the boron concentration,carbon concentration, oxygen concentration, BMD density, and epitaxialdefect (EP defect) density along with the pre-epitaxial process heattreatment condition. Table 1 shows the case of the low oxygenconcentration level and Table 2 shows the case of the high oxygenconcentration level.

TABLE 1 Density Single SIMS analytical result measuring result Testcrystal (atoms/cm³) Heat BMD EP defect No. section Boron Carbon Oxygentreatment (count/cm²) (count/wf) Category 1L Top 3.0 × 10¹⁸ — 1.4 × 10¹⁸— <1 × 10⁴  <10 Comparative portion Example (CE) 2L 3.0 × 10¹⁸ — 1.4 ×10¹⁸ A 2 × 10⁵ <10 CE 3L 3.0 × 10¹⁸ — 1.4 × 10¹⁸ B 5 × 10⁵ <10 CE 4L 3.0× 10¹⁸ 2.0 × 10¹⁵ 1.4 × 10¹⁸ — <1 × 10⁴  <10 Inventive Example (IE) 5L3.0 × 10¹⁸ 2.0 × 10¹⁵ 1.4 × 10¹⁸ A 4 × 10⁵ <10 IE 6L 3.0 × 10¹⁸ 2.0 ×10¹⁵ 1.4 × 10¹⁸ B 1 × 10⁶ <10 IE 7L Body 5.0 × 10¹⁸ — 1.2 × 10¹⁸ — <1 ×10⁴  <10 CE 8L portion 5.0 × 10¹⁸ — 1.2 × 10¹⁸ A 3 × 10⁵ <10 CE 9L 5.0 ×10¹⁸ — 1.2 × 10¹⁸ B 7 × 10⁵ <10 CE 10L 5.0 × 10¹⁸ 8.0 × 10¹⁵ 1.2 × 10¹⁸— <1 × 10⁴ <10 IE 11L 5.0 × 10¹⁸ 8.0 × 10¹⁵ 1.2 × 10¹⁸ A 1 × 10⁶ <10 IE12L 5.0 × 10¹⁸ 8.0 × 10¹⁵ 1.2 × 10¹⁸ B 3 × 10⁶ <10 IE 13L Tail 1.0 ×10¹⁹ — 9.0 × 10¹⁷ — <1 × 10⁴  >50 CE 14L portion 1.0 × 10¹⁹ — 9.0 × 10¹⁷A 3 × 10⁵ >100 CE 15L 1.0 × 10¹⁹ — 9.0 × 10¹⁷ B 5 × 10⁵ >100 CE 16L 1.0× 10¹⁹ 3.0 × 10¹⁶ 9.0 × 10¹⁷ — 3 × 10⁴ <10 IE 17L 1.0 × 10¹⁹ 3.0 × 10¹⁶9.0 × 10¹⁷ A 1 × 10⁶ <10 IE 18L 1.0 × 10¹⁹ 3.0 × 10¹⁶ 9.0 × 10¹⁷ B 2 ×10⁶ <10 IE

TABLE 2 Density Single SIMS analytical result measuring result Testcrystal (atoms/cm³) Heat BMD EP defect No. section Boron Carbon Oxygentreatment (count/cm²) (count/wf) Category 1H Top 3.0 × 10¹⁸ — 1.6 × 10¹⁸— 4 × 10⁴ <10 Comparative portion Example (CE) 2H 3.0 × 10¹⁸ — 1.6 ×10¹⁸ A 1 × 10⁶ >100 CE 3H 3.0 × 10¹⁸ — 1.6 × 10¹⁸ B 2 × 10⁶ >100 CE 4H3.0 × 10¹⁸ 2.0 × 10¹⁵ 1.6 × 10¹⁸ — 5 × 10⁴ >100 Inventive Example (IE)5H 3.0 × 10¹⁸ 2.0 × 10¹⁵ 1.6 × 10¹⁸ A 3 × 10⁶ <10 IE 6H 3.0 × 10¹⁸ 2.0 ×10¹⁵ 1.6 × 10¹⁸ B 5 × 10⁶ <10 IE 7H Body 5.0 × 10¹⁸ — 1.4 × 10¹⁸ — 3 ×10⁴ >100 CE 8H portion 5.0 × 10¹⁸ — 1.4 × 10¹⁸ A 1 × 10⁶ >100 CE 9H 5.0× 10¹⁸ — 1.4 × 10¹⁸ B 2 × 10⁶ >100 CE 10H 5.0 × 10¹⁸ 8.0 × 10¹⁵ 1.4 ×10¹⁸ — 4 × 10⁴ <10 IE 11H 5.0 × 10¹⁸ 8.0 × 10¹⁵ 1.4 × 10¹⁸ A 4 × 10⁶ <10IE 12H 5.0 × 10¹⁸ 8.0 × 10¹⁵ 1.4 × 10¹⁸ B 5 × 10⁶ <10 IE 13H Tail 1.0 ×10¹⁹ — 1.3 × 10¹⁸ — 3 × 10⁴ >100 CE 14H portion 1.0 × 10¹⁹ — 1.3 × 10¹⁸A 2 × 10⁶ >100 CE 15H 1.0 × 10¹⁹ — 1.3 × 10¹⁸ B 4 × 10⁶ >100 CE 16H 1.0× 10¹⁹ 3.0 × 10¹⁶ 1.3 × 10¹⁸ — 1 × 10⁵ <10 IE 17H 1.0 × 10¹⁹ 3.0 × 10¹⁶1.3 × 10¹⁸ A 3 × 10⁶ <10 IE 18H 1.0 × 10¹⁹ 3.0 × 10¹⁶ 1.3 × 10¹⁸ B 5 ×10⁶ <10 IE

As can be seen from Table 1, the high-level gettering ability can beexhibited in the test samples of the present invention in which thecarbon is doped in the pulling process of the CZ method. That is, theBMD density of not lower than 1×10⁴/cm² can be secured by performing thepre-epitaxial process heat treatment in either case where the testsamples are sliced from the top portion of the single crystal (Test Nos.5L and 6L) or the case where the test samples are sliced from the bodyportion (Test Nos. 11L and 12L), while the BMD density of not lower than1×10⁴/cm² can be secured in the test samples sliced from the tailportion (Test Nos. 16L to 18L) irrespective of the presence or absenceof the pre-epitaxial process heat treatment.

As can be seen from Table 2, the high-level gettering ability can beexhibited in the test samples of the present invention in which thehigh-concentration oxygen is doped. That is, the BMD density of notlower than 1×10⁴/cm² can be secured in any test samples sliced from thetop portion of the single crystal (Test Nos. 4H to 6H), sliced from thebody portion (Test Nos. 10H to 12H), or sliced from the tail portion(Test Nos. 16H to 18H) irrespective of the presence or absence of thepre-epitaxial process heat treatment.

For all the test samples by the present invention, because the EP defectdensity is lower than ten per substrate (wf), it is found that the EPdefect is remarkably decreased. It was confirmed that the observeddefect was not the epitaxial defect attributable to the substratecrystal defect.

On the contrary, the EP defect density is not lower than 50 or 100 persubstrate (wf) and almost all the observed EP defects are the epitaxialdefects attributable to the substrate crystal defects in any ofComparative Examples (Test Nos. 1H to 3H) sliced from the top portion,Comparative Examples (Test Nos. 7H to 9H) sliced from the body portion,and Comparative Examples (Test Nos. 13L to 15L and 13H to 15H) slicedfrom the tail portion.

Example 2

The silicon single crystal whose straight body portion has a diameter of300 mm was grown from a silicon raw material melt in which thehigh-concentration boron, carbon, and nitrogen are doped by the CZmethod, and the wafers were sliced from three sections composed of thetop portion, the body portion (intermediate portion), and the tailportion of the single crystal to produce test samples. At this point,the oxygen concentration of the test sample was separated into alow-concentration level and a high-concentration level.

As with the Example 1, the obtained test samples were separated into onegroup where the mirror polish finishing was treated to immediatelyperform the epitaxial growth process to the test sample and the othergroup where the epitaxial growth process is performed after thepre-epitaxial process heat treatment is performed, followed by themirror polish finishing, and the heat treatment was set at twoconditions A and B. In this case, the epitaxial process conditions, themeasuring conditions of the doping amounts, BMD density, and epitaxialdefect density, and the epitaxial defect evaluation conditions weresimilar to those of Example 1.

Tables 3 and 4 show the measurement results of the boron concentration,carbon concentration, oxygen concentration, BMD density, and epitaxialdefect (EP defect) density along with the pre-epitaxial process heattreatment condition. Table 3 shows the low oxygen concentration leveland Table 4 shows the high oxygen concentration level.

TABLE 3 Density Single SIMS analytical result measuring result Testcrystal (atoms/cm³) Heat BMD EP defect No. section Boron Carbon Oxygentreatment (count/cm²) (count/wf) Category 19L Top 3.0 × 10¹⁸ — 1.4 ×10¹⁸ — <1 × 10⁴  <10 Comparative portion Example (CE) 20L 3.0 × 10¹⁸ —1.4 × 10¹⁸ A 2 × 10⁵ <10 CE 21L 3.0 × 10¹⁸ — 1.4 × 10¹⁸ B 5 × 10⁵ <10 CE22L 3.0 × 10¹⁸ 2.0 × 10¹⁵ 1.4 × 10¹⁸ — 3 × 10⁴ <10 Inventive Example(IE) 23L 3.0 × 10¹⁸ 2.0 × 10¹⁵ 1.4 × 10¹⁸ A 3 × 10⁶ <10 IE 24L 3.0 ×10¹⁸ 2.0 × 10¹⁵ 1.4 × 10¹⁸ B 4 × 10⁶ <10 IE 25L Body 5.0 × 10¹⁸ — 1.2 ×10¹⁸ — <1 × 10⁴  <10 CE 26L portion 5.0 × 10¹⁸ — 1.2 × 10¹⁸ A 3 × 10⁵<10 CE 27L 5.0 × 10¹⁸ — 1.2 × 10¹⁸ B 7 × 10⁵ <10 CE 28L 5.0 × 10¹⁸ 8.0 ×10¹⁵ 1.2 × 10¹⁸ — 7 × 10⁴ <10 IE 29L 5.0 × 10¹⁸ 8.0 × 10¹⁵ 1.2 × 10¹⁸ A3 × 10⁶ <10 IE 30L 5.0 × 10¹⁸ 8.0 × 10¹⁵ 1.2 × 10¹⁸ B 4 × 10⁶ <10 IE 31LTail 1.0 × 10¹⁹ — 9.0 × 10¹⁷ — <1 × 10⁴  >500 CE 32L portion 1.0 × 10¹⁹— 9.0 × 10¹⁷ A 3 × 10⁵ >1000 CE 33L 1.0 × 10¹⁹ — 9.0 × 10¹⁷ B 5 ×10⁵ >1000 CE 34L 1.0 × 10¹⁹ 3.0 × 10¹⁶ 9.0 × 10¹⁷ — 1 × 10⁵ <10 IE 35L1.0 × 10¹⁹ 3.0 × 10¹⁶ 9.0 × 10¹⁷ A 2 × 10⁶ <10 IE 36L 1.0 × 10¹⁹ 3.0 ×10¹⁶ 9.0 × 10¹⁷ B 3 × 10⁶ <10 IE

TABLE 4 Density Single SIMS analytical result measuring result Testcrystal (atoms/cm³) Heat BMD EP defect No. section Boron Carbon Oxygentreatment (count/cm²) (count/wf) Category 19H Top 3.0 × 10¹⁸ — 1.4 ×10¹⁸ — 4 × 10⁴ >100 Comparative portion Example (CE) 20H 3.0 × 10¹⁸ —1.4 × 10¹⁸ A 1 × 10⁶ >100 CE 21H 3.0 × 10¹⁸ — 1.4 × 10¹⁸ B 2 × 10⁶ >100CE 22H 3.0 × 10¹⁸ 2.0 × 10¹⁵ 1.4 × 10¹⁸ — 7 × 10⁴ <10 Inventive Example(IE) 23H 3.0 × 10¹⁸ 2.0 × 10¹⁵ 1.4 × 10¹⁸ A 5 × 10⁶ <10 IE 24H 3.0 ×10¹⁸ 2.0 × 10¹⁵ 1.4 × 10¹⁸ B 7 × 10⁶ <10 IE 25H Body 5.0 × 10¹⁸ — 1.2 ×10¹⁸ — 3 × 10⁴ >100 CE 26H portion 5.0 × 10¹⁸ — 1.2 × 10¹⁸ A 1 ×10⁶ >100 CE 27H 5.0 × 10¹⁸ — 1.2 × 10¹⁸ B 2 × 10⁶ >100 CE 28H 5.0 × 10¹⁸8.0 × 10¹⁵ 1.2 × 10¹⁸ — 1 × 10⁵ <10 IE 29H 5.0 × 10¹⁸ 8.0 × 10¹⁵ 1.2 ×10¹⁸ A 4 × 10⁶ <10 IE 30H 5.0 × 10¹⁸ 8.0 × 10¹⁵ 1.2 × 10¹⁸ B 6 × 10⁶ <10IE 31H Tail 1.0 × 10¹⁹ — 9.0 × 10¹⁷ — 3 × 10⁴ >1000 CE 32H portion 1.0 ×10¹⁹ — 9.0 × 10¹⁷ A 2 × 10⁶ >1000 CE 33H 1.0 × 10¹⁹ — 9.0 × 10¹⁷ B 4 ×10⁶ >1000 CE 34H 1.0 × 10¹⁹ 3.0 × 10¹⁶ 9.0 × 10¹⁷ — 3 × 10⁵ <10 IE 35H1.0 × 10¹⁹ 3.0 × 10¹⁶ 9.0 × 10¹⁷ A 7 × 10⁶ <10 IE 36H 1.0 × 10¹⁹ 3.0 ×10¹⁶ 9.0 × 10¹⁷ B 1 × 10⁷ <10 IE

As can be seen from Tables 3 and 4, in the test samples by the presentinvention in which the carbon and the nitrogen are doped, the BMDdensity of not lower than 1×10⁴/cm² can be secured in any test samplessliced from the top portion of the single crystal (Test Nos. 22L to 24Land 22H to 24H), sliced from the body portion (Test Nos. 28L to 30L and28H to 30H), or sliced from the tail portion (Test Nos. 34L to 36L and34H to 36H) irrespective of the presence or absence of the pre-epitaxialprocess heat treatment.

And for all the test samples by the present invention, because the EPdefect density is lower than ten per substrate (wf), it is found thatthe epitaxial defects attributable to the substrate crystal defects arenot generated.

In contrast, the EP defect density is not lower than 100, 500, or 1000per substrate (wf) respectively in Comparative Examples (Test Nos. 19Hto 21H) sliced from the top portion, Comparative Examples (Test Nos. 25Hto 27H) sliced from the body portion, or Comparative Examples (Test Nos.31L to 33L and 31H to 33H) sliced from the tail portion, and almost allthe observed EP defects are the epitaxial defects attributable to thesubstrate crystal defects.

As described above, according to the silicon semiconductor substrate andthe production method thereof by the present invention, in any epitaxialwafer substrate, the uniform and high-level gettering ability isobtained irrespective of the slicing positions from the silicon singlecrystal while the generation of the epitaxial defect can be suppressed,by doping carbon or carbon along with nitrogen during the pullingprocess of the CZ method or alternatively by performing the appropriateheat treatment prior to the epitaxial process. Therefore, thepermissible upper limit (concentration margin) which is restricted bythe formation of the ring-shaped OSF region can be much higher toexhibit the excellent gettering ability, and the epitaxial wafer inwhich the epitaxial defect attributable to the substrate crystal defectis not generated can be produced to thereby improve the crystalproduction yield remarkably, and thus the silicon semiconductorsubstrate by the present invention can widely be used as the siliconsemiconductor substrate which becomes the epitaxial wafer.

1. An epitaxial wafer which includes an epitaxial layer on a surface of a silicon semiconductor substrate, wherein the silicon semiconductor substrate is grown by the Czochralski method on a condition that a ring-shaped region of oxygen induced stacking fault emerges in a crystal surface over a whole length of a straight body portion of a pulled silicon single crystal, and wherein the silicon semiconductor substrate is sliced from the silicon single crystal, which has dopants consisting of carbon and boron, with boron ranging from 1×10¹⁷ to 1×10¹⁹ atoms/cm³ and carbon ranging from 1×10¹⁵ to 2×10¹⁶ atoms/cm³ (ASTM F123-1981), and wherein the number of defect to be observed on the surface of the epitaxial wafer is not more than 10 count/wf.
 2. The silicon semiconductor substrate used for an epitaxial wafer according to claim 1, wherein the silicon semiconductor substrate is sliced from the silicon single crystal which is grown while an oxygen concentration ranges from 9×10¹⁷ to 16×10¹⁷ atoms/cm³ (ASTM F121-1979).
 3. The silicon semiconductor substrate used for an epitaxial wafer according to claim 1, wherein a BMD (bulk micro defect) density in a cross section of a silicon substrate sliced from said silicon single crystal is not lower than 1×10⁴ count/cm² in any region over the whole length of the straight body portion of the single crystal.
 4. A silicon semiconductor substrate used for an epitaxial wafer, wherein an epitaxial defect attributable to a crystal defect of the silicon semiconductor substrate does not exist in a surface of an epitaxial layer in any region over the whole length of the straight body portion of the single crystal when said epitaxial layer is formed on the silicon semiconductor substrate according to claim
 1. 